The invention relates to a method for producing a microelectronic component of sandwich construction, and an inverter that includes the microelectronic component.
Such inverters can be used to convert direct current into alternating current, and are needed particularly for controlling motors. Power modules, of the kind used so far in inverters, as a rule include a substrate, on which a number of power chips as well as components for triggering, evaluating, protecting, and the like are disposed side by side. The substrate, for example, can be a filled plastic film, which is disposed on an aluminum base plate. A conductor track system, typically made of copper, is located on the plastic film. The connection among the individual components and between them and the conductor tracks is effected by so-called thick wire bonding. In so-called econopacks, bonding is not done to the conductor tracks but rather directly to terminal pins. Both in econopacks and in standard modules, terminal pins are needed for bonding, and they are complicated and expensive to make because they must be manufactured in a special production step with special tools.
Because all the system components are disposed side by side in the same plane, the known power modules are relatively large, and the connection paths spanned by bond wires are relatively long. In such an arrangement, a very poor power-inductance layout is obtained, and complicated technology is required. To prevent dynamic countercoupling, one additional control source is needed for the control terminal. Wire bonding is also a weak point in terms of alternating load stresses, which impairs the reliability of the power modules.
German Patent Application DE 34 06 528 A1 teaches the fixation of components when components are being soldered to conductor tracks. After soldering, the components should remain bonded to the conductor tracks as firmly as possible. To compensate for any possible mechanical stresses, compensation pieces made of molybdenum can optionally be provided.
U.S. Pat. No. 4,922,376 discloses the use of spring elements with components for contacting the components in a way that enables repair of a failed contact. If a contact fails, it can be repaired by loosening a screw connection and replacing the applicable spring element.
U.S. Pat. No. 5,203,075 discloses a method for connecting a first, flexible conductor track substrate to a second conductor track substrate. The first substrate has conductive balls, that are soldered to soldering points on the second substrate.
U.S. Pat. No. 4,855,867 discloses a flexible conductor track substrate onto which semiconductor chips are mounted that are electrically conductively connected by balls to a fixed circuit board.
It is accordingly an object of the invention to provide a method for producing a microelectronic component of sandwich construction that can be used particularly as a power module and that is simple and space-saving in design, and that provides an improved behavior in response to thermal mechanical stresses. The microelectronic component can be produced economically and simply, and it offers high flexibility in terms of the disposition of individual components. Furthermore, a lower-inductance makeup of the power and triggering part is assured.
With the foregoing and other objects in view there is provided, in accordance with the invention, a microelectronic component having a sandwich construction, comprising:
a first substrate having a first conductor track plane;
a plurality of semiconductor chips having first sides electrically connected to the first conductor track plane, and second sides opposite the first sides;
a second substrate having a second conductor track plane; and
an electrically conductive, flexible adhesive disposed between and electrically connecting the second conductor track plane and the second sides of the plurality of semiconductor chips.
In accordance with an added feature of the invention, an additional electrically conductive, flexible adhesive is disposed between the first conductor track plane and the first sides of the plurality of semiconductor chips. The additional electrically conductive, flexible adhesive provides the electrical connection of the first sides of the semiconductor chips to the first conductor track plane.
In accordance with an additional feature of the invention, balls are disposed in the additional electrically conductive, flexible adhesive.
In accordance with another feature of the invention, balls are disposed in the electrically conductive, flexible adhesive.
In accordance with a further feature of the invention, the first substrate and the second substrate are ceramic materials.
In accordance with a further added feature of the invention, the ceramic materials are selected from the group consisting of aluminum oxide and aluminum nitride.
In accordance with a further additional feature of the invention, the ceramic material is a thick film ceramic material and the first conductor track plane is a fired on conductor track plane.
In accordance with another added feature of the invention, the ceramic material is a thick film ceramic and the first conductor track plane is a direct copper bonded conductor track plane.
In accordance with another added feature of the invention, the ceramic material is a thick film ceramic and the first conductor track plane is an active metal brazed conductor track plane.
In accordance with another added feature of the invention, the first substrate is a thick film ceramic material and the first conductor track plane is a fired on conductor track plane.
In accordance with another added feature of the invention, the first conductor track plane is a material selected from the group consisting of copper and silver.
In accordance with another added feature of the invention, the first substrate is a thick film ceramic and the first conductor track plane is a direct copper bonded conductor track plane.
In accordance with another added feature of the invention, the first substrate is a thick film ceramic and the first conductor track plane is an active metal brazed conductor track plane.
In accordance with another added feature of the invention, the first substrate has a side opposite the first conductor track plane with a first metal layer.
In accordance with another added feature of the invention, a heat sink is disposed on the first metal layer.
In accordance with another added feature of the invention, the second substrate has a side opposite the second conductor track plane with a second metal layer.
In accordance with another added feature of the invention, a heat sink is disposed on the second metal layer.
In accordance with another added feature of the invention, the second substrate has holes formed therethrough.
In accordance with another added feature of the invention, the semiconductor chips are power chips.
In accordance with another added feature of the invention, electronic components selected from the group consisting of triggering, evaluation, and protective components are also included.
In accordance with another added feature of the invention, the electronic components are disposed on the second substrate.
In accordance with another added feature of the invention, the second substrate has holes formed therethrough, and the electronic components are electrically connected to the second conductor track plane through the holes.
In accordance with another added feature of the invention, the first substrate and the second substrate are clamped together.
In accordance with another added feature of the invention, the second substrate has at least two retaining openings formed therethrough, and the first substrate includes at least two retainers for releasably engaging the retaining openings.
In accordance with another added feature of the invention, the retainers are snap hooks.
In accordance with another added feature of the invention, the second substrate is separated into a plurality of individual regions.
In accordance with another added feature of the invention, the second substrate is a flexible substrate.
In accordance with another added feature of the invention, the second substrate is a polyimide film.
In accordance with another added feature of the invention, the semiconductor chips include two isolated gate bipolar transistors and two diodes.
In accordance with another added feature of the invention, the semiconductor chips are interconnected as an inverter.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a method for producing a microelectronic component having a sandwich construction, which comprises:
providing a first substrate having a first conductor track plane;
providing a plurality of semiconductor chips having first contact faces electrically connected to the first conductor track plane, and second contact faces opposite the first sides;
providing a second substrate having a second conductor track plane with contact points;
securing electrically conductive balls to the contact points of the second conductor track plane using an electrically conductive, flexible adhesive;
applying an electrically conductive, flexible adhesive to the second contact faces of the plurality of semiconductor chips; and
joining the first substrate and the second substrate together.
With the foregoing and other objects in view there is also provided, in accordance with the invention, an inverter, comprising:
a first substrate having a first conductor track plane;
a plurality of semiconductor chips having first sides electrically connected to the first conductor track plane, and second sides opposite the first sides;
a second substrate having a second conductor track plane; and
an electrically conductive, flexible adhesive disposed between and electrically connecting the second conductor track plane and the second sides of the plurality of semiconductor chips.
The invention relates to a microelectronic component having sandwich construction that includes a first substrate with a first conductor track plane and a second substrate with a second conductor track plane. Disposed between the two substrates are a plurality of semiconductor chips, that are contacted to both conductor track planes. In the multichip module of the invention, contacting of the semiconductor chips is effected from the surface of the semiconductor chips that is remote from the first substrate, to the second conductor track plane by fixed contacting means. The sandwich construction provides a substantially more-compact and more space-saving design than if a single substrate were used. The flexibility in the disposition of the individual components is markedly greater.
The term xe2x80x9cfixed contacting meansxe2x80x9d between the semiconductor chips and the conductor track plane should be understood to mean that the contacting is not performed with bond wires. On the contrary, contacting means are provided that are less sensitive to thermal mechanical stresses than soldered connections. Suitable contacting means those that include an electrically conductive, flexible adhesive. Any conductive adhesives that are typically used in microelectronic components can be used.
Electrically conductive spring elements can also be provided, in particular metal spiral or leaf springs.
The contacting can be performed using electrically conductive balls. This contacting technique is known in principle and is generally called the xe2x80x9cball grid techniquexe2x80x9d. The electrically conductive balls preferably comprise a metal material, such as lead, lead solder, tin, tin-antimony solder, copper, or other metals, such as silver, or their alloys. It is provided that the balls be secured with the aid of an electrically conductive adhesive and in particular with a flexible adhesive.
Using the inventive method, the microelectronic components of the invention can be produced by first applying electrically conductive balls to the contact points of the second conductor track plane. The conductive balls are preferably applied through a perforated baffle. Excess balls are removed. It is especially advantageous if the balls are spaced closely together. In the final method step, the first and second substrates are joined to the chips and the electrically conductive balls applied to them, so that the chips and the second conductor track plane are contacted.
Alternatively, it is possible for the electrically conductive balls to be applied to the surface of the semiconductor chips. Once the sandwich structures according to the invention have been produced, the interstices between the first and second substrate and optionally between further substrate planes are preferably filled with a dielectric material. Silicone resin or silicone gel, for instance, is suitable.
The semiconductor chips used in the microelectronic component of the invention can in principle be secured to the first substrate in an arbitrary way and contacted to the first conductor track plane. Preferably, the semiconductor chips are soldered onto the first substrate. Preferably, the semiconductor chips are connected to the first substrate and the first conductor track plane and to the second substrate and the second conductor track plane in the same manner. In that case, semiconductor chips with surfaces that can be soldered on both sides are needed. Such chips are known in the art. By way of example, their surfaces can be provided with a nickel-gold layer, which allows the application of solder.
To manufacture the substrates, various substrate materials typically used for microelectronic components are suitable, such as plastic films or laminates, optionally in a composite structure with other materials. Ceramic materials are especially suitable, such as those of aluminum oxide or aluminum nitride ceramic. In a composite structure with a corresponding conductor track plane, ceramic substrates such as a thick-film ceramic, for instance, in which a conductor track system, which can comprise copper, silver or the like, is fired onto or into the substrate. Other suitable composite systems of substrates and conductor tracks are those made by DCB (direct copper bonding) or AMB (active metal brazing) techniques. Such ceramic substrates have considerably better thermal conductivity than plastic substrates, which makes them especially suitable for power modules.
To improve heat dissipation, a metal layer, for instance of copper, can additionally be applied to the side of the first and/or second substrate opposite the conductor track plane. Such a metal layer serves as a heat spreader and can be coupled with a heat sink (such as a metal plate), to further improve heat dissipation.
Good heat dissipation is especially necessary whenever the inventive microelectronic component is equipped with power chips. If these chips are exposed to constant load changes, they alternatingly heat up and cool off. Under some circumstances, the result is that the sandwich system of the invention functions, and the connections between semiconductor chips and the conductor track plane or planes are mechanically stressed considerably. If electrically conductive adhesives are used, this stress is less critical than with pure soldered connections, and particularly with soldered connections using electrically conductive balls.
In a variant, the second substrate is cut apart into a plurality of individual regions that are movable relative to one another and that can follow motions in the system caused by temperature changes.
In a preferred embodiment of the invention, the second substrate is entirely made of a flexible material. A substrate of plastic film, preferably polyimide film, is especially suitable.
If a flexible film is used as the second substrate, then preferably no further components are disposed on it, although that would also be possible. It is more advantageous to dispose the further components around the sandwich module of the invention. Nevertheless, this requires no additional terminal pins in the sandwich module of the invention, because electrical contacting can be done directly to the conductor track that is disposed on the flexible substrate film. All that is required for this purpose is that the film be bent upward somewhat at the edges.
The microelectronic components of the invention, because of their sandwich construction, allow versatile design in terms of the disposition of the individual components used.
Along with the semiconductor chips, the microelectronic components can for instance include triggering, electronic evaluation, and/or protective components, of the kind usually used in microelectronic components. Examples are pulse generators, pulse repeaters, pulse width modulators, controllers, optocouplers, and the like. Other possible components are choppers and output inverters, for instance.
These components can either all be disposed on the first substrate, or some of them may be disposed on the first and some on the second substrate and optionally on further substrates, if the microelectronic component of the invention includes more than two substrate layers lying one above the other. Disposing components on multiple planes has the advantage that the microelectronic component of the invention can be designed especially compactly. Furthermore, triggering, protection or evaluation electronics can be positioned directly above the respective associated semiconductor component, making a very simple and expedient design attainable. In such a case, contacting is preferably with the through holes that are mounted in the second substrate.
As noted, however, the component of the invention is not limited to merely two substrates one above the other. On the contrary, additional planes can be present in the microelectronic component.
If ceramic substrates and particularly thick-film ceramic are used, then it is also possible to dispose the logic part, for example, controller ICs, PWM ICs (IC=integrated circuit; PWM=pulse wide modulation) in the same plane as the power chips. An integrated shield, for instance in the form of metal layers on the first and second substrates, is then provided in the microelectronic component of the invention, and this shield protects the logic part in regard to electromagnetic compatibility (EMV).
An especially preferred embodiment of the microelectronic component of the invention includes two switching transistors, preferably IGBTs (isolated gate bipolar transistors), and two diodes and can for instance be used for converting direct current into alternating current. An inverter which includes a microelectronic component of the invention is also the subject of the invention.
In inverter operation, depending on the type of load, either the switching transistor or the diode becomes hotter, and thermal mechanical stresses thus occur in the microelectronic component. Such stresses can cause the contacting means between the first and second conductor track plane to be destroyed. This problem occurs quite generally in microelectronic components of the kind that use power chips, as has already been described above. To overcome this problem, the microelectronic component of the invention is preferably embodied such that contacting of the semiconductor chips to the second conductor track plane and optionally also to the first conductor track plane is done with electrically conductive spring elements.
In general, contacting the semiconductor chips to the second conductor track plane by electrically conductive spring elements already suffices to absorb the thermomechanical stresses. The spring elements are preferably glued to the semiconductor chip surface and the conductor track planes with an electrically conductive adhesive, or in cases of high power consumption are soldered to them.
In a preferred embodiment, the spring elements are embodied as closely wound spiral springs with annularly closed ends. In such an embodiment, the individual springs cannot catch in one another. It is thus possible for the spring elements needed for a microelectronic component of the invention to be shaken into a suitable soldering mold in a single step, and then soldered to the semiconductor chips or the conductor track plane.
The length of the spring element is suitably selected to effect compensation for deviations in thickness between the various chips in a component of the invention and changes in spacing caused by thermomechanical stresses between the first and second substrates. Preferably, the spring elements are long enough so that the contacting means between the first and second substrates are embodied without additionally inserted contact blocks.
In a variant of the microelectronic component of the invention, one end of the spring element is soldered to the semiconductor chip, and the second end is soldered to the conductor track plane which is disposed on the second substrate. Solder pads can be applied to the contact points of the conductor track plane in the way already described, for instance by being printed on the contact points.
In another variant, the ends of the spring elements remote from the semiconductor chips are glued or soldered into recesses or through openings in the second substrate. In this variant, the spring elements are accordingly as a rule longer than in the first variant, in which the solder pads end at the surface of the second substrate. Thus the spring elements are long enough that adequate contacting and an adequately secure fastening in the recesses or through openings of the second substrate is assured, even under the influence of thermomechanical stresses.
In addition to the spring elements that connect the semiconductor chips to the second conductor track plane, other spring elements can be disposed between the first and second conductor track planes or the first and second substrates. These additional spring elements can also be glued with an electrically conductive adhesive, or can be soldered. If the spring elements engage recesses or through openings in the second substrate, then flow soldering is a preferred way of securing the spring elements.
In principle, either single examples or all of the above described types of contacting means and securing or fastening can be combined with one another in a given microelectronic component.
To assure a stable, simple fastening between the first and second substrate, the two substrates are preferably clamped together. To that end, two or more retainers are expediently provided on one of the two substrates and they releasably engage associated recesses or through openings in the other substrate. To assure a secure hold, the retainers can be provided with snap hooks on their ends or other barblike devices that prevent them from slipping out of the recesses or through openings. The described features can be employed accordingly on further planes, if the microelectronic component has such additional planes.
For the type of fastening of the first and second substrate mentioned, a microelectronic modular component that is a portion of the microelectronic component of this invention and is also the subject of this invention is especially suitable. The microelectronic modular component of the invention includes a first substrate with a first conductor track plane and many semiconductor chips, which are contacted to the first conductor track plane. For contacting the semiconductor chips to a further conductor track plane, in the manner described above, electrically conductive spring elements or electrically conductive balls are mounted on the semiconductor chips. In a preferred refinement, the microelectronic modular component includes retainers for clamping the microelectronic modular component to the second substrate, which substrate has the described recesses or through openings for receiving the retainers.
The microelectronic modular component can also include a metal coating as a heat spreader and/or a heat sink for dissipating the heat generated by the semiconductor chips. Furthermore, the semiconductor chips and the surrounding surface of the first substrate can be covered with a dielectric composition, such as silicone resin or silicone gel, as has also already been described. The thickness of the dielectric composition applied is preferably such that in the finished microelectronic component the interstice between the first and second substrates is filled up as completely as possible.
The microelectronic modular component of the invention is preferably prefabricated to the extent that the final user merely has to clamp it together with a suitable second substrate and then make the contacting means to the second substrate.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for producing a microelectronic component of sandwich construction, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.